1. Field of the Invention
The present invention relates to a positioning substrate for a semiconductor process, which is used for performing a teaching operation on a transfer mechanism for transferring a target substrate in a semiconductor processing system. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or an LCD substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In the process of manufacturing semiconductor devices, a wafer is subjected to various semiconductor processes, such as film formation, etching, oxidation, diffusion, and so forth. In these processes, owing to the demands of increased miniaturization and integration of semiconductor devices, the throughput and yield involving these processes need to be increased. In light of this, there is a semiconductor processing system of the so-called cluster tool type, which has a plurality of process chambers for performing the same process, or a plurality of process chambers for performing different processes, connected to a common transfer chamber. With this system, various steps can be performed in series, without exposing a wafer to air.
One type of this processing system includes, at its front, a port structure for placing a semiconductor wafer cassette. Each wafer in the cassette is taken into the system by a transfer mechanism, and is subjected to an alignment operation by an alignment device, and then is transferred into a load-lock chamber, whose pressure is adjustable between a vacuum and atmospheric pressure. Then, the wafer is transferred into a common vacuum transfer chamber, to which a plurality of vacuum processing apparatuses are connected therearound. The wafer is sequentially transferred into the vacuum processing apparatuses from the common transfer chamber at the center, so that it is subjected to processes in the apparatuses. After the wafer is processed, it is returned, for example, into the original cassette through the same route.
Such a processing system has a single or a plurality of transfer mechanisms, by which a wafer is automatically transferred from one place to another. Each transfer mechanism has a holding pick, which is, for example, extensible/contractible, swingable, and movable up and down. The holding pick directly holds a wafer, and moves horizontally to a transfer position, so that the wafer is transferred to a predetermined place.
It is necessary to prevent the holding pick and a wafer placed thereon from interfering or colliding with other members, while the transfer mechanism is moving. It is also necessary for the holding pick to properly pick up a wafer placed at a certain place, and transfer it to a destination, and delivers it to an appropriate position, with high positional accuracy, such as within ±0.20 mm.
Accordingly, after a system is assembled or extensively altered, a so-called teaching operation is performed on the control section, such as a computer, for controlling its transfer mechanism. The teaching operation is performed to teach important positions, such as a place in its movement route where the holding pick of the transfer mechanism delivers a wafer W, as coordinate positions to the control section.
The teaching operation is performed for the positional relationships between the holding pick and almost all the places for wafer delivery, and their coordinate positions are stored into the control section. For example, these positional relationships include the positional relationship between the holding pick and a cassette; the positional relationship between the holding pick and each of the shelves of the cassette in the vertical direction for picking up wafers; the positional relationship between the holding pick and the table of a load-lock chamber; the positional relationship between the holding pick and an alignment device, the positional relationship between the holding pick and the susceptor of a vacuum processing apparatus; and the like. The driving system of each transfer mechanism is provided with an encoder or the like built therein for specifying the movement position.
FIGS. 23A and 23B are plan views showing two examples of holding picks having different shapes for a transfer mechanism. FIG. 23A shows a holding pick 13 with a bifurcate shape, whose distal ends 13A and 13A each form an essentially semi-circular arc. FIG. 23B shows a holding pick 14 also with a bifurcate shape, whose distal ends 14A and 14A each form an essentially right-angled flat line.
Next, an explanation will be given of a positioning substrate used for the teaching operation. FIGS. 24 and 25 are a plan view and a sectional view, respectively, showing a conventional positioning substrate corresponding to the holding pick shown in FIG. 23A. Other than the positioning substrate shown in FIG. 24, a positioning substrate disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 8-64547 is also known.
As shown in FIGS. 24 and 25, this conventional positioning substrate 2 has a substrate body 4, which is like a circular plate, and is formed from a transparent resin material, such as polycarbonate resin. The substrate body 4 has the same diameter as an actual semiconductor wafer to be processed in the processing system. The substrate body 4 is provided with a positioning cut, such as a notch 6, formed at a position on the peripheral edge. The substrate body 4 is also provided with a reference hole 8 at the center, which is formed of a through-hole having a predetermined inner diameter.
At the center and periphery on the surface of the substrate body 4, circular and ring light-shielding coatings 10 and 12 of, e.g., organic coating, are formed, respectively, to correspond to detection target positions by optical sensors for detecting the presence or absence of a wafer. The light-shielding coatings 10 and 12 allow the optical sensors disposed at the necessary positions in the processing system to recognize the presence of the substrate body 4. Furthermore, on the surface of the substrate body 4, a pair of thin reference lines 16 are formed to correspond to the outer contour (the lateral side 13B or distal end 13A) of the holding pick 13 shown in FIG. 23A.
When a teaching operation is performed, the coordinate positions of places to be taught in the entire system are first obtained from designed values, using a point on the movement route of a transfer mechanism as the absolute reference. These are inputted and stored into the control section as provisional coordinate positions. In this case, each of the provisional coordinate positions is inputted with a predetermine margin such that a holding pick does not interfere with another member.
Then, on the basis of each provisional coordinate position, the transfer mechanism is driven to move the holding pick to a position near a teaching reference position. Then, the operation of the transfer mechanism is switched to a manual mode (which may be simply referred to as “manually”), and, for example, the holding pick 13 shown in FIG. 23A is brought into contact with a positioning substrate 2, which is placed in advance on a predetermined position in a cassette. Then, the transfer mechanism is manually operated with visual observation, so that the contour of the holding pick 13 accurately aligns with the reference lines 16 of the positioning substrate 2. When they align with each other, coordinate data obtained at this time is stored as its coordinate position in the control section.
When a positioning operation is performed for the movement of the transfer mechanism relative to an alignment device, it is performed as follows. First, with visual observation, the positioning substrate 2 is placed on the holding pick 13, such that its contour accurately aligns with the reference lines 16. Then, the holding pick 13 is manually moved to place the positioning substrate 2 on the rotary table of the alignment device. At this time, a reference hole 8 formed at the center of the positioning substrate 2 is caused to accurately align with the central position of the rotary table. Coordinate data obtained at this time is stored as its coordinate position in the control section. The manual mode (“manually”) described above means inputting a movement direction (+/−) and a movement amount into a control section by a keyboard or joystick, to operate a transfer mechanism.
When a positioning operation is performed relative to a table or susceptor of a load-lock chamber or a vacuum processing apparatus, it is performed as follows. First, the positioning substrate 2 is placed at the center of the table or susceptor. Then, the corresponding holding pick 13 is manually moved so that the holding pick 13 accurately aligns with the reference lines of the positioning substrate. Coordinate data obtained when they align with each other is stored as its coordinate position in the control section.
Incidentally, a processing system of this kind is used to perform a micro-processing or the like on a semiconductor wafer. Accordingly, it is necessary to prevent particles or impurities from entering the processing system, as much as possible. However, as described above, the positioning substrate 2 is made of a resin material, such as polycarbonate resin, and the light-shielding coatings 10 and 12 formed thereon are made of components mainly of organic substances. As a consequence, during a teaching operation, fine pieces from the substrate body 4 or light-shielding coatings 10 and 12 are scattered as particles in the processing system, and cause problems, such as organic contamination on a semiconductor wafer. Particularly, in recent years, as devices are becoming more and more highly miniaturized and integrated, and the line width has decreased to sub-micron level, it is demanded to solve the problems described above as early as possible.
As shown in FIG. 26, a plurality of, e.g., about 25 at most, semiconductor wafers are accommodated in a cassette 22, which is a box-like container 18 made of Teflon (registered TM) with shelves 20 layered at regular intervals on the inner wall. Each semiconductor wafer W has a very small thickness of, e.g., about 0.8 mm, although it depends on the wafer size. Accordingly, when the wafer W is supported by shelves 20 at opposite ends, it is inevitable for the wafer W to bend downward with a certain warp amount H1, as shown in FIG. 26.
A semiconductor wafer W used in a processing system and the positioning substrate 2 made of polycarbonate resin for a teaching operation differ in stiffness, and thus they also show different warp amounts H1. During a teaching operation, the positioning substrate 2 is placed on each pair of shelves 20, and a height position of the holding pick 13 for accessing the substrate 2 is stored as a coordinate position for each pair of shelves 20. However, as described above, since they show different warp amounts H1, problems arise, e.g., wafer W transfer errors occur at worst.
The intervals H2 between the shelves 20 are preset as small as possible, e.g., about 10 mm, to hold a number of wafers W therein, and thus their coordinate positions have to be set with high accuracy.
Particularly, the warp amount H1 is small when the wafer size is 6 inches (15 cm) or 8 inches (20 cm), but it is considerably large when the wafer size is 12 inches (30 cm). In the latter case, the difference in the warp amount is not negligible.
It may be conceivable to increase the stiffness of the positioning substrate, so that the positioning substrate 2 shows the same warp amount H1 as semiconductor wafers W. However, in order to increase the stiffness, the positioning substrate 2 has to be thicker, thereby causing a change in distance relative to a wafer placed on upper or lower side. Besides, since the positioning substrate 2 becomes heavier, the arm of the transfer mechanism undesirably shows a different warp amount, when the holding pick 13 of the transfer mechanism holds the positioning substrate 2.
Furthermore, where a teaching operation is performed again after a processing apparatus or the like of a processing system is repaired, a part of the system may be not sufficiently cooled but still have residual heat. In this case, the positioning substrate 2 made of resin that is not heat-resistant may cause problems, such as deformation by the part having residual heat.